Inter-band carrier aggregation is performed in a Release 11 (Rel-11) Long Term Evolution (LTE) system, and in order to avoid interference with an adjacent carrier Time Division Duplex (TDD) system in a different band, an LTE cell in the different band may perform Carrier Aggregation (CA) using a different TDD uplink and downlink sub-frame configuration. For a TDD CA User Equipment (UE) with a low capability, its simultaneous uplink and downlink operation over different carriers, for example, simultaneous reception of downlink data over a Component Carrier (CC) 1 and transmission of uplink data over a CC 2 in the same sub-frame, can not be supported.
The technology of carrier aggregation will be introduced below.
In wireless communication systems of the LTE and earlier, there is only one carrier in a cell, and there is a maximum bandwidth of 20 MHz in the LTE system, as illustrated in FIG. 1.
In a Long Term Evolution-Advanced (LTE-A) system, there are required peak rates of the system up to downlink 1 Gbps and uplink 500 Mbps significantly improved over the LTE system. The required peak rates can not be achieved by only a carrier with a maximum bandwidth of 20 MHz. Thus the LTE-A system has to extend the bandwidth available to the user equipment, and in view of this, the technology of carrier aggregation has been introduced where a plurality of consecutive or inconsecutive carriers under the same evolved NodeB (eNB) are aggregated together to serve the UE simultaneously and provide the required rates. These aggregated carries are also referred to as component carriers. Each cell may be a component carrier, and cells (member carriers) under different eNBs can not be aggregated. In order to ensure the UE of the LTE to be capable of operating over each aggregated carrier, the maximum bandwidth of each carrier is no more than 20 MHz. The CA technology of the LTE-A is as illustrated in FIG. 2 where there are four carriers that can be aggregated under an LTE-A eNB, and the eNB can communicate data with the UE simultaneously over the four carriers to improve the throughout of the system.
In the LTE system, there is a radio frame of 10 ms and a sub-frame of 1 ms in both FDD and TDD schemes. For each TDD radio frame, seven TDD uplink and downlink sub-frame configurations are defined as depicted in Table 1:
TABLE 1Uplink and downlinksub-frameSub-frame numberconfiguration01 234567890DSUUUDSUUU1DSUUDDSUUD2DSUDDDSUDD3DSUUUDDDDD4DSUUDDDDDD5DSUDDDDDDD6DSUUUDSUUD
Where D represents a downlink (DL) sub-frame, U represents an uplink (UL) sub-frame, and S represents a special sub-frame of the TDD system, for example, the sub-frames are configured as DSUUDDSUUD in the case of the configuration 1.
For the LTE TDD system, the UE may feed back, in an uplink sub-frame, acknowledgement (ACK) or non-acknowledgement (NACK) information corresponding to a plurality of downlink sub-frames, that is, after demodulating and decoding data in a downlink sub-frame n−k, the UE feeds back in an uplink sub-frame n, to the eNB, signaling (that is, ACK/NACK information) of whether to retransmit the data in the downlink sub-frame, kεK, K: {k0, k1, . . . kM−1}, where the values of the set K depend upon an uplink and downlink configuration of the system and a particular sub-frame number as depicted in Table 2:
TABLE 2Uplink and downlink sub-frame Sub-frame number (n)configuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, ————8, 7,——64, 63——7, 6, 116, 55,—————44——12, 8, 6, 5,——————7, 114, 75——13, 12, ———————9, 8, 7, 5, 4, 11, 66——775——77—
Here a plurality of radio frames are arranged sequentially, that is, if the last sub-frame in a radio frame a is k, then the first sub-frame in a radio frame a+1 is k+1, and Table 2 depicts K corresponding to each uplink sub-frame by way of an example with only one radio frame, where n−k<0 represents a downlink sub-frame in a preceding radio frame.
In the existing carrier aggregation system, the UE feeds back UL ACK/NACK at the foregoing timing in each aggregated cell, and the corresponding feedback is performed in a primary cell (PCell).
For transmission of uplink data, the eNB needs to transmit in the downlink an ACK/NACK feedback, which is carried over a Physical Hybrid Automatic Repeat Request (HARQ) Indicator Channel (PHICH). For a Frequency Division Duplex (FDD) system, uplink and downlink sub-frames coexist, that is, there is a PHICH resource per sub-frame, so there is a relatively fixed timing relationship between the downlink ACK/NACK feedback and the corresponding uplink data, where ACK/NACK feedback information corresponding to uplink data in the n-th sub-frame is transmitted in the (n+4)-th downlink sub-frame. For a TDD system, there are different numbers of uplink and downlink sub-frames in different TDD sub-frame configurations, such a case may arise that ACK/NACK feedback information of a plurality of uplink sub-frames are transmitted in the same downlink sub-frame, where ACK/NACK feedback information corresponding to uplink data in the n-th sub-frame is transmitted in the (n+k)-th downlink sub-frame, and the value of k is as depicted in Table 3:
TABLE 3TDD uplink and downlink sub-frame Uplink sub-frame number (n)configuration0123456789047647614646266366646656646647
In existing carrier aggregation, the UE receives DL ACK/NACK information at the foregoing timing in each aggregated cell, and the corresponding feedback is received over the PHICH channel in the cell in which a UL grant scheduling a Physical Uplink Shared Channel (PUSCH) is transmitted.
In the system of the LTE Rel-11 or later, in order to avoid interference with another TDD system, there is such network deployment that different TDD uplink and downlink sub-frame configurations may be used in a plurality of LTE cells in different bands as illustrated in FIG. 3 where a carrier 1 is in a band A, and a carrier 2 is in a band B, and a cell 1 and a cell 2 are cells respectively over the carrier 1 and the carrier 2. A TDD uplink and downlink sub-frame configuration of the cell 1 is the configuration 0, and a TDD uplink and downlink sub-frame configuration of the cell 2 is the configuration 1 different from that of the cell 1. If the UE intends to perform carrier aggregation for these two cells, then such a case may arise that there are different TDD uplink and downlink configurations of the aggregated cells for the UE as illustrated in FIG. 4, and this network deployment scheme using different TDD configurations may result in inconsistent transmission directions of different cells in the same sub-frame, for example, the sub-frame 4 and the sub-frame 9 illustrated in FIG. 4 are uplink sub-frames in the cell 1 and downlink sub-frames in the cell 2. For some UE with a low capability, a capability to operate simultaneously in a plurality of cells may be absent in such sub-frames.
In summary, there has been no solution so far in the prior art to how the UE incapable of supporting simultaneous uplink and downlink transmission communicates data in the carrier aggregation system using different TDD uplink and downlink configurations.